The referenced application, and corresponding German Patent Publication, describes a method and system to reproduce video signals recorded on video recording tape in the form of slanting tracks. This system permits bidirectional change in reproduction time with respect to recording time, in effect providing for slow-motion or accelerated or fast-motion reproduction of events recorded at a standard recording speed. The video image of a complete frame is recorded in a plurality of adjacent tracks; usually, the frames are interlaced so that a half-image is recorded on adjacent tracks. The recording speed is that usually or normally used, the tape being passed in a spiral path over a cylindrical body in which a recording head on a rotating head wheel is rotating. Upon psssing the tape over the cylindrical body, and rotating the recording head, the plurality of adjacent tracks will be formed extending at an angle with respect to the longitudinal axis of the magnetic tape, thereby storing signal information representative of the video image. The speed of movement of the head wheel during recording and reproduction is about the same. It is the transport speed of the magnetic tape which is changed. Since the magnetic tape moves at a speed different from that of the recording speed, the magnetic heads will sense and transduce magnetically recorded signals into electrical signals which do not at all times correspond to the tracks on the tape, as recorded. The magnetic heads will scan the tape at an angle which is different from the angle of inclination of the recorded tracks. This difference angle may cause the heads to scan at an angle which crosses adjacent tracks, depending on the speed and direction of the difference in transport speed of the tape. To reconstruct a complete television image, it is necessary to store only those signals which occur during the time portions, during scanning, which satisfy the signal read-out requirements, the stored signals then being read out in accordance with television reproduction standards.
In practical use of the system described in the cross-referenced application, and patent it has been found that usual criteria for the recognition of signals to be stored are not sufficient for recognition of the signals themselves; these criteria, are, primarily, the amplitude of the signal, or the amplitude of the carrier frequency if the signals are recorded on a carrier. Due to the narrow width of the gap beteen adjacent tracks on the magnetic tape, it is difficult to distinguish between signals of adjacent tracks since the amplitude of the reproduced signals change upon transition from one track to the next by only a slight amount. It is thus very difficult, and sometimes impossible, to reliably detect transition from one track to the other by sensing drop in signal level. Additionally, addressing each one of the lines already in recording requires substantial circuitry in the recording system.